Spool-type valves for controllably diverting the flow of fluids are well known. In a typical spool valve, a hollow piston, or “spool,” having a plurality of radial ports through the spool wall is slidably disposed within a cylindrical body that is also provided with a plurality of internal annular grooves and radial ports extending through the body wall. The spool is variably positionable within the body to cause selected ports in the spool to be aligned with grooves and ports in the body, thereby permitting flow of fluid from outside the body through first aligned ports into the interior of the spool and out through second aligned ports. A plurality of different flow paths typically is possible by positioning the spool at a plurality of different axial positions within the body. Typically, the spool is connected to a linear solenoid actuator, whereby the spool may be axially positioned by signals from a controller such as a computerized engine control module, although other actuations such as pneumatic and hydraulic are within the scope of the invention as described below.
A common usage for an oil-control spool valve is to variably actuate engine control subsystems such as camshaft phasers and variable valve activation (VVA) mechanisms, and multi-step or valve deactivation mechanisms. In a two step valve mechanism, for example, the mechanism selects the lift profile (low or high) of an intake valve camshaft using a hydraulically activated roller finger follower (RFF).
In a simple configuration of this example, a spool valve supplies high pressure oil, typically from an engine-driven oil pump, to activate the RFF, and shuts off the oil supply to deactivate and drain pressure from the RFF. However, it is desirable that in RFF-deactivation mode the oil supply not be completely shut off, as other components of the valve train, such as camshaft lobes and rocker arms, continue to require flow of oil for lubrication. In the prior art, continued lubrication may require separate valving and/or complicated porting.
What is needed is an oil control valve assembly that is switchable not simply between on and off modes but between a pressure high enough for RFF activation and a controlled pressure low enough for lubrication but insufficient for RFF activation.
What is needed further is means for instantaneously switching of the oil supply from high-pressure mode to low-pressure mode.